1. Field of the Invention
The present invention generally relates to data networks and voice-over-internet protocol (VoIP) data packets. More specifically, the present invention relates to a system and method for efficiently distributing VoIP media to very large and/or geographically dense ad-hoc dispatch calls, such as Push-to-Talk group communications, in a wireless telecommunication network.
2. Description of the Related Art
In a wireless network, the users of wireless communication devices communicate over an air-interface to a central computer. This may be done directly, as in the case of a wireless LAN in an office environment, or it may be done through cellular infrastructure equipment, as in the case of a wireless telephone application. One type of personal communication system is a push-to-talk (PTT) system. A PTT communication connection is typically initiated by a single button-push on the wireless device that activates a half-duplex link between the speaker and each member device of the group and once the button is released, the device can receive incoming PTT transmissions once the button is released. In some arrangements, the PTT speaker will have the “floor” where no other group member can speak while the speaker is speaking. Once the speaker releases the PTT button, any other individual member of the group can engage their PTT button and they will have the floor. A specific PTT group of recipient devices for the communicating wireless device is commonly set up by the carrier and the wireless devices themselves do not allow the modification of the group, i.e. to include or drop individuals from the group, or to purposely direct a communication to be received by any fewer members than the entire group.
The typical PTT call involves two users who are rarely located within the same telecommunication sector such that communication and replication of the communication is propagated easily over the existing telecommunication infrastructure. However, a small but very important fraction of push-to-talk calls involve a larger number of call participants, some of whom may also be located within the same sector; public-safety disaster scenarios are one example. In such scenario, the maintenance of the PTT communications within the group all located on the same telecommunication resource is difficult and inefficient. These systems will use “trunks” of the telephone network and standard channel allocation that devote individual circuits for each call participant, thus limiting system scalability.
In existing “wired” networks, it is known to use a “broadcast” of data over a broadcast channel such that data is sent to all potential receivers and the receiver can determine whether or not the broadcast media applies to it. Applications such as LAN TV, desktop conferencing, corporate broadcasts, and collaborative computing, require data transmission in a “point-to-multipoint” fashion, which is, transmitting data to multiple recipients simultaneously. Such applications would require a tremendous amount of network bandwidth to be effectively implemented using the point-to-point technique. For example, using a traditional point-to-point transmission scheme would require the same information to be transmitted n times, where n represents the number of recipients. The bandwidth required to accomplish such a task would grow in proportion to the number of computers receiving the transmission. Such an approach is infeasible for applications where large data transmissions, such as audio and video, need to be sent to a large number of recipients. To effectively implement the transfer of large quantities of data in a point-to-multipoint network, a broadcast design is used wherein data is broken into packets, each packet addressed to a “broadcast address,” rather than addressing multiple copies of each packet to each recipient desiring the information. However, the network must generally send the information packets throughout the entire network so that anyone desiring reception of the information can “listen” to the broadcast address and receive the information. Thus, the raw propagation of broadcasting packets everywhere is a significant use of network resources if only a small group of recipients desire the information.
To overcome this problem, a technique known as Internet Protocol (IP) multicast has been developed for use in wired IP networks. With IP multicasting, applications can send one copy of each data packet and address it to a group of recipients that wish to receive the information generated by an application. This technique addresses data packets to a group of recipients rather than to individual recipients, and it relies on the network to forward the data packets only to “paths” that have a sub-network that needs the information, i.e., a sub-network having at least one recipient desiring the particular IP multicast. One example of a subnetwork is a local broadcast network, such as an Ethernet LAN.
It is known to encapsulate voice data within IP data packets, this method commonly referred to as “VoIP”. In common Ethernet wireless networks, such as an IEEE Standard 802.11(b) network, the network allows for wholesale broadcasting of IP packets. However, within the constraints of wireless networks, it would be desirable to limit multicast transmissions to a specific geographic area having at least one receiving user desiring reception because of the disadvantage of flooding the wireless network with packets. Presently, in order to transmit an IP multicast transmission in a wireless network, the transmission must be sent to all end devices, regardless of whether or not the multicast transmission is desired, which burdens all resources of the PTT group whether or not the receiving device is able to receive VoIP packets. Moreover, such efficient broadcasting of VoIP packets would allow a very geographically dense group of PTT devices to communicate despite the limited telecommunication resources. It is thus to such a system and method of efficiently broadcasting voice data packets to the wireless telecommunication devices of a PTT communication group that the present invention is primarily directed.